Through the course of Final Fantasy 9, you'll find Stellazio coins. In
case you're stuck, here's a full list of where they can be found...

Aries

On the ground on the first floor of the Windmill in
Dali.

Cancer

In the overturned crate in the Burmecia Suburb.

Gemini

Throw 130 Gil into the fountain at the Treno Gate.

Taurus

On the ground near the item shop in the Treno slums.

Scorpio

On the ground in the lower level of Quan's dwelling.

Virgo

On the guestroom floor of the Black Mage Village Inn.

Libra

Next to the fountain in Madain Sari.

Leo

On the ground in the Neptune Room of Alexandria's West
Tower.

Sagittarius

On the ground in the Lindblum Shopping Area during the
rebuilding.

Capricorn

In the water in the entrance room of Daguerreo.

Aquarius

In a chest in the entry hall of Ipsen's Castle.

Pisces

In a chest in the core area of the airship Invincible.

Ophiuchus

After giving the first 12 to Queen Stella, find the
13th in Quan's Dwelling.

Present each and every Stellazio coin to Queen Stella (in Treno). For
each one, she'll give you a prize. Here's the list (in order)...

1,000 Gil

Pheonix Pinion

2,000 Gil

Blood Sword

5,000 Gil

Elixer

10,000 Gil

Black Belt

20,000 Gil

Rosetta's Ring

30,000 Gil

Robe of Lords

After presenting her with the first 12 coins, she'll return them to you
and ask that you use them as hints to find the last Stellazio coin, the
Ophiuchus. After collecting all 13 Stellazio coins, give them back and
you'll recieve the Hammer.